Add the ability to disable and enable headers

[eduardolat]

trafficstars

It would be very useful if the headers can be disabled and re-enabled (maybe with checkboxes). This should work with the "Save headers" option.

Use case: Imagine you have two "Authorization" headers, and you want to switch between the two, maybe for testing administrator and regular user authentication, and just enable it or disable instead of copy-paste every time.